text:
Why do English-speaking pilots and ATC say "Niner" instead of "Nine"?
Besides the fact that it's now a standard, why do American-English-speaking pilots and ATC say "Niner" instead of "Nine"?  None of the other numerals are pronounced in an atypical fashion.
For what was "Nine" being mistaken that resulted in the "Niner" standard being adopted?

Not all - only the properly trained ones :-)

Hmm... I'd say the fact that it's a standard is why pilots use it. It also sounds a lot less weird to a native English speaker than the tree/fower/fife stuff. Those just sound like a non-native incorrectly trying to pronounce three, some unknown word, and five, respectively. :)

It's ICAO standard. And certainly with the US military. Actually using it is another thing. And if you've ever used shortwave to communicate you'd get that big "A-Ha".

@radarbob Can you elaborate on the shortwave reference?

Due to the nature of shortwave reception can be weak and/or have lots of noise. Speaking phonetically helps tree-mendously. And often we'd have to phonetically spell, e.g. "Whisky Hotel Alpha Tango".

"Nein, the nine is mine". <-- a bit contrived, but it should illustrate the problem.

According to Wikipedia:

The pronunciation of the digits 3, 4, 5, and 9 differs from standard English – being pronounced tree, fower, fife, and niner. The digit 3 is specified as tree so that it is not pronounced sri; the long pronunciation of 4 (still found in some English dialects) keeps it somewhat distinct from for; 5 is pronounced with a second "f" because the normal pronunciation with a "v" is easily confused with "fire" (a command to shoot); and 9 has an extra syllable to keep it distinct from German nein 'no'.

The phonetic alphabet is not a random selection of words. It was created very carefully taking dialects into account, so as not to confuse any of the letter with possible mispronunciations. Although they are "English" words, the choices were made with the world in mind.
As mentioned on the same article:

The final choice of code words for the letters of the alphabet and for the digits was made after hundreds of thousands of comprehension tests involving 31 nationalities.

Where do English-speaking pilots and ATC say "tree" for "three"?

@RockPaperLizard, it happens inconsistently in the U.S.  I say tree, and about half the ATC in the area do as well. I can't say the percentage of pilots that do in the Pacific Northwest but it's probably under 25%.

@RockPaperLizard Inconsistently in the UK also.  I too use the stylised versions depending on quality of comms, perceived workload/experience of controller and amount of traffic.

@RockPaperLizard Germany as well. Germans struggle with the English "th", it often comes out as "sri" as mentioned above. This is why it is consistently taught as "tree" in Germany for aviation purposes, when English is used in ATC/(A)FIS communication. The Aviation.SE blog will have a series on stuff like this... we are working on it. :)

@RockPaperLizard If you go through this entire video, you will understand the reason very well.

@RockPaperLizard: Because the difference is subtle (more so than with "niner"), you can't really tell, can you? ;-) BTW, the reasoning is the same for Germans saying "zwo" instead of "zwei" (to distinguish it from "drei").

That wiki para is completely unreferenced...

@RockPaperLizard I've known Irishmen who pronounce 3 as "tree". It wouldn't surprise me if the whole country has a similar dialect.

Adding the extra syllable to "foh-er" and "niner" means that the vowel patterns OH, UH, OO, EE, OH-IH, AY, IH, EH-EH, EY, AY-IH, are all distinct even without any consonants.  I don't know whether radio static played a role in the choice of phonetics, but I think vowels are often less likely to be misinterpreted than consonants.  As for "t" versus "th" for "3", even if the ideal pronunciation were an English "th", some non-English-speakers might say something closer to that if asked to say "t" than if asked to say "th".

Surely, "niner" helps to distinguish 9 from 5. I'd've thought that most of the time, context would make it obvious whether you meant fire or 5 or whether you were saying 'no' in German or 9. But it's surely as easy to mistake a 9 for a 5 as it is to mistake a B for a D, say.

@Au101 This is why they went ahead and dont use single letters by themselves, but have the ICAO alphabet: Bravo and Delta.

@SentryRaven Well that's what I mean. Sorry if I wasn't clear. I would think at least one benefit of using niner is that it helps distinguish 9 from 5. In the same way that using bravo and delta prevents confusion between B and D. So I was just trying to say that it would make sense to get around the problem of having similar sounding numbers - 5 and 9 - by saying niner; much as we get around the problem of having similar sounding letters. Removing such confusion being the purpose of the alphabet, niner would be useful in avoiding, say, confusion between 5,000 ft and 9,000 ft

@Au101 Hmm... I'm not sure about that. At least to me, nine and five don't sound similar at all. Seems like they'd be difficult to confuse, even on a poor-quality radio link. One funny (and kind of ironic) thing about getting in the habit of saying 'niner' is that I've actually had it cause confusion when using it in non-aviation circles (e.g. reading product keys over the phone or similar.)

@reirab I'm glad you mentioned that you don't consider "five" and "nine" to sound alike.  I was thinking the same thing, but was too shy to mention it, because that opinion seems to be in the minority.  The main similarity I hear is the vowel sound, and perhaps that's enough to cause confusion.

Surely the "niner" dates all the way back to WWII? A lone survivor pilot coming back from the front didn't want anyone thinking he was a German.

I'm really sick of people pronouncing three as tree. Sree is way better than tree.

@RockPaperLz-MaskitorCasket: I think the issue isn't that "five" and "nine" sound alike, but rather that static bursts may sound similar to "f" or "v".  Something that sounds like an "n" probably is an "n", but something that sounds like an "f" or "v" might be something else that was hit with a burst of static.

Just curious: what would be the problem of pronouncing "three" as "sri"?

@EricDuminil perhaps its too close to the Spanish si which means Yes, weirdly the opposite case of niner!

The reasons I've heard behind the pronunciations:

Three / Tree:
Some non-native English speakers have trouble both pronouncing and understanding the "TH" sound.  Tree is better pronounced and better understood by all people, regardless of accent.

Five / Fife:
Much of aviation has a military history.  On a poorly heard transmission "Five" can sound a lot like "Fire", which is both a military command to "shoot", and an aviation emergency!   "Fife" avoids that ambiguity.

Nine / Niner:
German is a commonly spoken language, and "Nein" (pronounced like "Nine" in English) is "No" in German.  To keep it clear that this is a digit and not a negative-reply, "Niner" is distinct from the "Nine"

I've heard that explosives/demolitions engineers skip "Five" for the same reason, but I can't confirm that with fact, only hearsay.

There's a joke of a german pilot asking "May I get local QHN?" ATC: "Nine, nine, nine".. "Und warum nein?"

I truly appreciate your answer.  Even if partially anecdotal, it provides significant insight.

„nein” is “no” in German. “nine” is only pronounced (almost) the same way.

I've heard explosive users skip 4 to avoid confusion with "fire".  "Five" and "Nine" have the same vowel, so the 2-syllable "Niner" helps distinguish those two (as does the soft "f" in "Fife", which is more distinct from "n" than "v" would be).

@TobySpeight: "Five" could also come out "Five-uh" whose vowels would be close to those of "niner".

At least in the Royal Navy, the word Fire is reserved for when a self-sustaining combustion reaction is ongoing on your vessel. If you want guns to launch things at someone, you say Shoot!.

@gusto2 And nobody wonders warum the German didn't say "warum nicht" instead of "warum nein"?

The standard answer is that “nine” could be mistaken for German “nein”.
Another possibility is that all the digits have a different vowel (or vowel pair) from each other except “nine” and “five”.  Changing “nine” to “niner” adds another vowel sound, which may help distinguish them when radio reception is poor.

"Niner" is spoken for the numeral 9 to avoid it being mistaken for 5.

This would be better as a comment once you gain enough reputation.

@dalearn, what is your basis for saying this would be better as a comment?  It answers the question, and answers are frowned upon in comments.


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Has any aircraft ever been designed such that it could descend safely with no control input?
Has there ever been any aircraft of any type that could glide safely with no control input simply based on the way the frame of the aircraft was designed?
I was trying to think of requirements for building an aircraft that would be accessible to the masses and the first thing I thought of was safe landing in the event of engine failure or other catastrophic mechanical breakdown.
It seems to me that it would be possible using modern composites to create some type of aircraft whose default flying configuration is a safe, slow descent. NOT including parachute equipped such as cirrus, has any such craft been designed/flown?

Descending safely is easy, it's landing safely that's the real challenge :-) No amount of aerodynamics will help you if you glide straight into a brick wall.

The aircraft behavior will also depend on center of gravity, which can vary depending on payload.

A well designed paper airplane exhibits those characteristics.

@abelenky: A well designed paper airplane exhibits a Reynolds number higher than any existing manned aircraft.

You might also want to look into AutoLanding AutoPilot. If you are wanting to design a system to be "fool-proof", I'd say a huge component would be computer controlled/assisted systems.

I've heard (but never seen corroborated) that the Antonov An-2 was able to be trimmed fully aft in the event of an engine failure, and that it would descend with minimum forward speed - and a vertical speed that approximates that of a parachutist.

Don't worry, @MatthewPeters, they'll soon develop a better fool...

@FreeMan haha! Indeed. That reminds me of a quote I saw once that said, "Programming is a race between programmers to produce bigger, better, more idiot-proof systems and the universe to produce bigger and better idiots. So far, the universe is winning." I think this could be generalized equally well to all of engineering.

Every paper plane and parachute.

Broadly speaking most (if not all) light GA aircraft can "glide safely with no control input" - aircraft are generally designed to have positive dynamic stability, such that they will return to a stable equilibrium condition (e.g. "level cruise flight") in the face of most modest upsets. Once configured for cruise flight they can maintain it with little input from the pilot (and if equipped with even a basic autopilot "little input" can often be reduced to "no input" for extended periods of time).
Whether or not the engine is producing power is largely irrelevant here, save for the fact that if the engine isn't producing power you will eventually be descending.
Positive stability alone will not make aviation "accessible to the masses" however, nor will autopilots: As with driving a car or riding a motorcycle there are certain "aeronautical decision-making" skills which a pilot must possess in order to safely fly (and land) an aircraft when everything goes right. If you introduce problems (like engine or instrument failures) the need for a real live pilot becomes even more critical: technology can not yet replace the critical decision making capabilities of a trained human mind.

Particularly in regard to your question about a default flight mode of a controlled descent, even a simple autopilot can already do what you describe: Planes will continue to fly the last autopilot-commanded heading or route until they run out of fuel, at which point they'll start descending (while still attempting to fly the programmed profile).
What they cannot do is select a suitable landing site, update their flight profile, and fly themselves to a safe landing. For that to happen without human intervention requires a huge amount of luck.
In a particularly famous example of this kind of luck a Piper Comanche "landed" itself in a field after running out of fuel, the pilot being unconscious at the time due to carbon monoxide poisoning. The pilot survived and in fact literally walked away from the accident scene, and the aircraft in question is, as best I can determine, still flying.

I vaguely recall there was a plane that landed intact in a corn field after the pilot baled out or ejected. Must try to find that.

http://en.wikipedia.org/wiki/Cornfield_Bomber The "Cornfield Bomber" was a Convair F-106 Delta Dart, operated by the 71st Fighter-Interceptor Squadron of the United States Air Force, that made an unpiloted landing in a farmer's field in Montana, suffering only minor damage, after the pilot had ejected from the aircraft. The aircraft, recovered and repaired, was returned to service, and is currently on display at the National Museum of the United States Air Force.

"technology can not yet replace the critical decision making capabilities of a trained human mind."  So... no Google self-flying planes in the near future?

@Michael: I would say self-flying planes are very much in the near future. Perhaps marginally more likely is self-flying helicopters, as choppers are more manoeuvrable but harder to pilot safely.

Then there was that jet that flew on (chartered by some golfer, IIRC) with no one conscious (or alive, again IIRC) until it ran out of fuel.

The golfer was Payne Stewart.  The plane was operating on autopilot when, apparently, there was a loss of cabin pressure and all on-board died.  The plane continued on until it ran out of fuel and crashed.

@Michael We have self-flying (and even self-landing) planes now - the question is what happens when something goes wrong (e.g. the engine stops turning)? Flying from point A to point B and landing on a guaranteed-clear runway is pretty complicated, but finding a spot big enough to put your aircraft when you've got no thrust and all you can do is descend is substantially harder :)

@Michael: Cars have the luxury that they can always slam on the brakes if something fails. Aircraft can't.

@JanHudec On the other hand, aircraft have the luxury that they don't (usually) have other vehicles, deer, people, etc. suddenly jumping out in front of them or unpredictably changing speed near them. Honestly, in a lot of ways, I'd say self-driving cars are actually a bigger challenge than self-driving airplanes (which is probably why airplanes that could be programmed to fly themselves to their destination safely existed decades before cars that could be programmed to drive themselves safely to their destination... and the latter are still usually limited to very slow speeds.)

No deer, but geese.  And fewer cyclists to drive safely around.

@reirab - You pinned it. The biggest problem in self-driving cars is the relative density of obstacles on the ground versus in the air, and thus the miniscule reaction time required for collision avoidance. Aircraft have minimum clearances in excess of a mile; cars can be inches from each other even at speed.

@KeithS Yep, It's always fun to drive through a construction zone with narrowed lanes at 70 mph while separated laterally from a semi by less than a foot... and with a slightly smaller separation from a concrete barrier on the other side.

Not really a plane, but Autogyro are really safe even when motor shutdowns.
http://en.wikipedia.org/wiki/Autogyro
For having tried one, when motor stops, it just descends slowly (maybe 1m/s max), and you just have to make little corrections before landing, to convert vertical speed to horizontal speed. It's really like an "air bike"

Welcome to Aviation:SE! Re "Not really a plane": The OP used aircraft multiple times, not airplanes. I think you've nailed a really good example in your answer.

The autogyro is a great example of an "inherently safe" design: it'll come down gently (even without an autopilot) in most circumstances. You'd still want a pilot to make sure it lands in a convenient spot though: Winding up in the middle of a lake wouldn't be good if there's a conveniently-empty parking lot nearby...

Indeed, during an early test of a Pitcairn autogiro (as they spelled it), one of the rotor blades came loose and departed the aircraft. The test pilots, feeling the strong vibration and assuming the craft was about to disintegrate, bailed out. However, it flew in circles for several minutes and then landed itself in the corn field they were flying over with only minor damage to the landing gear.

True for the classic autogiros of very low disk loading. A present-day gyro, in vertical autorotation, will hit the ground at about 1500 fps. Survivable, but barely, and quite a crash...

You might want to look at the Antonov An-2.  The leading edge slats are spring-loaded.  If your airspeed falls below about 40 mph, they deploy.  With them deployed and minimal/no power, your speed drops to about 25 mph and your "sink rate" is so low that the aircraft can perform a controlled descent and landing without damaging the gear (depending on the surface you land on, naturally).  The plane has no defined "stall speed," meaning that you can pass out, pull the controls full aft, run out of fuel and make a relatively uncontrolled descent, yet you might actually survive.
This seems to be the closest to what you're asking for.

You are in some regards introducing a few questions here

I was trying to think of requirements for building an aircraft that
  would be accessible to the masses

Bringing aviation to the masses is only in part related to the aircraft its self. For what its worth the Piper Cherokee 140 can be had for less than most new cars and has what has been called "Very Benigin" handling some might even say making it to safe. The plane like most GA planes glides very easily and practicing engine outs is routine to get your license. Which brings up the more important point. The current US regulations set fourth by the FAA makes it much tougher to fly a plane (although sport pilot has helped this) than it does to drive a car. To be honest it does not take that much to legally drive a car here in the US. Learning to fly an airplane is a significantly larger task, it takes an investment (anywhere from 7K-15K depending on local flight school costs) and more time than learning to drive a car. This is really what keeps the masses from flying.
For what its worth new planes are not cheap not only because they are expensive to build but because FAA type certs are not easy to come buy.

and the first thing I thought of was safe landing in the event of
  engine failure

Engine failure is, (assuming there is no fire involved) a recoverable situation as long as there is an open field or even a local parkway to put the craft down. Small planes (and most planes for that matter) glide fairly well and can be maneuvered under glide with ease.

or other catastrophic mechanical breakdown.

The problem with this is that most of the clean handling characteristics of small GA planes are predicated on the fact that the plane is as it should be. There are a million and one things that can break but may will cause a situation that will alter the handling or flight characteristics of a plane like asymmetric flap deployment or snapped control cables/disabled flight controls or even critical air frame failures like the 2008 incident involving a Pilatus PC-6.

could glide safely with no control input simply based on the way the
  frame of the aircraft was designed

As has been mentioned most GA planes (at least the slower trainers) are made to return to a safe attitude to some extent. It should be noted that this often requires some kind of minimum altitude and many accidents happen at low altitude when the plane simply does not have time to recover. Some of this may also be effected by things like trim which if set to its limits has an effect on the planes handling.

Aircraft for the unskilled pilot have a long history. Provided the plane is basically stable, there are several conditions for a safe dead-stick landing:

Wing loading must be low. This will keep the rate of descent to a safe level, so the pilot does not need to flare up and slow the descent for landing.
Aerodynamic efficiency must not be too high, so that the plane does not "float" in ground effect for a long distance.
For true hands-off, you have to avoid phugoid oscillation. Flown in this condition, many planes will slowly begin to nod slowly up and down, the oscillations eventually growing to disastrous levels.

First off the block was the tailless swept-wing biplane developed by British pioneer J W Dunne. It was also capable of automatically recovering from a stall - assuming you could somehow get it into one. In 1910 it became the world's first certified stable airplane, an event witnessed by none other than an astonished Orville Wright. The Burgess-Dunne was built under license in the US and from time to time other Americans such as Smith and Waterman based their "safety aeroplanes" on it. Its main undoing is that, being tailless, it has a small CG range, which requires some experience to live with.
There are plenty of more conventional types around. Perhaps the great "everyman" classic was the de Havilland Moth biplane of the golden age.

Has there ever been any aircraft of any type that could glide safely
  with no control input simply based on the way the frame of the
  aircraft was designed?

Absolutely.  While many aircraft have inadequate roll stability to truly descend safely with no pilot input, especially if some turbulence is present, some aircraft do have an ample amount of roll stability as well as pitch stability.  An example would be a Rogallo-style hang glider with ample sweep to the leading edges.  Placing the point of connection between the pilot's body and the aircraft structure well below the aircraft CG helps to lower the effective the CG of the glider-pilot system which further increases both pitch and roll stability via the "pendulum effect", yet hang gliders have also been witnessed to fly remarkably stably when accidentally launched off a hill with no pilot attached.
Powered hang-glider-like aircraft ("trikes") can be, and have been, built on the same principles.  This miniature radio-controlled model of a Rogallo-wing "trike" is extremely stable and easily capable of descending for a prolonged period, even in turbulent air, with no pilot input.  Note that in this case the "trike" unit with motor and batteries is rigidly fixed in place (the position only changes when the servos move), so the "pendulum effect" is even further enhanced-- the CG of the aircraft is far below the wing.
(The "pendulum effect" is based on the fact that the drag vector, and the aerodynamic sideforce vector generated by a sideslip, both tend to exert stabilizing torques when they act above the CG of the aircraft or the aircraft-pilot system.  The "pendulum effect" has also been caused the "keel effect", though this is somewhat misleading as the stabilizing action of buoyancy on a boat with a weighted keel is independent of sideslip. Some people dislike the term "pendulum effect" as well because it implies that the aerodynamic center of the aircraft is acting as some sort of a fixed pivot point, about which the weight vector or the G-load vector exerts a torque-- this is not really an accurate depiction of what is going on.)
Note that when a pilot hangs by a single flexible strap and exerts no force with his arm muscles, his body weight acts as if it is located at the point where the strap connects to the aircraft.  Some early hang gliders had this connection point located well below the "keel tube" to enhance pitch and roll stability; this practice has now been discontinued because it the resulting short "hang strap" increases the muscle force that a pilot must exert to shift his weight a given distance to the side. On the other hand, in paragliders the pilot hangs by multiple suspension lines which act essentially like rigid struts due to the triangular geometry involved; in this case the pilot's body weight no longer effectively acts as if it were located at the point where the lines connect to the wing, but rather at its actual location-- which places the CG of the whole system far below the wing and creates a powerful "pendulum effect" which leads to strong roll stability, despite the anhedral geometry of the actual wing.
Paraglider pilots have often flown in clouds using only minimal instrumentation, such as a magnetic compass.  Clearly this is only possible in an aircraft with strong intrinsic pitch and roll stability.  On February 4 2007 paraglider pilot Ewa Wisnerska, flying without oxygen, was unintentionally lifted into a thunderstorm and survived an accidental climb in a thunderstorm to 32,000 feet above sea level followed by a descent back to earth.  She was unconscious for over an hour, with her body encased in ice.  When she regained consciousness her aircraft was in a stable descent.
Of course, there is an entire discipline of model-airplane-flying called "free flight".  These models rise up, and then return to earth, usually landing safely, without any control input of any kind.  It is instructive to examine their configuration.  They almost invariably have dihedral and rather small vertical fins, and usually have a high-wing configuration.
Related ASE questions and answers:
(Q) What is the Keel Effect?
(Q) Does "pendulum effect" apply to hang gliders or any aircraft?
(A) Does "pendulum effect" apply to hang gliders or any aircraft?
(Q) Why are high-wing aircraft more stable?
(Q) How does the "pendulum effect" affect biplanes??
(Q) Does the dihedral effect happen during coordinated flight?

Very brave to mention "pendulum effect" in spite of much passion of some folks reaction to it.  May I suggest "dihedral effect" works better, as even an anhedralled hang glider will have its center of drag above the CG, and also sweep, resulting in a net "dihedral effect".  +1 answer otherwise.

Several mythical effects have been ascribed to the poor pendulum. At least this answer names it after a valid effect.

@RobertDiGiovanni -- consider the paraglider case specifically.  I prefer to avoid "dihedral effect" because in a sideways flow the upwind wing actually has a lower angle angle-of-attack than the downwind wing, due to the anhedral shape of the actual wing, and likewise with some hang gliders with visible anhedral.  I prefer to keep the effect of sideforce  (and drag force) acting above the CG as a separate thing, which might legitimately said to contribute to a larger combined effect called something like "effective dihedral".

@RobertDiGiovanni -- so in short I guess I would prefer to say "effective dihedral" includes the effects of various things such as actual dihedral (a geometry that induces a difference in angle-of-attack during wings or other pairs of matched surfaces during a sideslip), and sweep, and "pendulum effect" or "keel effect" (i.e. the effect of sideforce and drag force acting above the CG).  I think we've talked about this before; I better stop now or the comments will get moved.

@quiet flyer you are correct in distinguishing dihedral/anhedral and side force drag torque so ... +1 for your work.

Future edit: paragraph starting with word "Note" has an extra word "it" in second sentence.

Future edit-- paragraph in parentheses-- "caused" should be "called".

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What is the minimum stopping distance for a 747-400?
Im looking at purchasing  disused 747-400:

The aircraft will be stripped of all seats and other non essential items.
The aircraft will be then flown to my property in Victoria, Australia and perform a one off landing.
The landing distance would be between 1500-2300 feet.

Can this be done?

Are you willing to land gear up? :-)

"Sure. Once." -- Flying into a local airport that can handle a 747 and then dismantling and trucking the aircraft would be substantially safer though...

A 747 was landed in Longreach which has a 6500 ft runway. I seem to recall that this was considered a major endeavour. https://www.youtube.com/watch?v=tDJOtwGUAcI

Boeing has flown 747s into Renton Airport during the late 60s, which has a 5000 ft runway.

If they can land a C-130 on an aircraft carrier without a tailhook, you can land a 747 wherever the hell you want as far as I'm concerned. https://www.youtube.com/watch?v=ar-poc38C84

@HCBPshenanigans that doesn't make sense to me. The C-130 was designed to take off and land from very short airfields, while I don't believe the 747 was. Also, the USS Forestal was ~1000 feet, not that much shorter than the runway in question

@raptor True. Was more of an excuse to post that!

Interesting question. I think it could be done in the right conditions if you are willing to accept some damage and depending on the runway.
Is the runway level or uphill/downhill? If you could land uphill in a high wind that was almost all headwind, I believe you could either do it or would overrun the runway at a low speed. Airplanes slow down really quickly going uphill.
A stripped 747-400 probably weighs about the same as a 747-400 freighter, maybe a little less because the freighter has the equipment for loading and securing pallets. If you're using Firefox or Chrome (IE won't work), click on any aircraft at 747.terryliittschwager.com and you'll see the empty weight is around 362,000 lbs (you can change the weight unit to kilos there if you wish).
I used to land at Tel Aviv with only 15,000 lbs of fuel in 747-200s. The -400 burn rate may be a little higher, but let's use that. You would have to be comfortable with being totally committed to landing, with the possibility of only one quick go-around. Maybe you could even cut the 15,000 down to 10,000 with no go-around possibility?
Let's use 375,000. Vref for a -200 at 400,000 (lowest figure in the table I have) is 118 kts. In that area Vref decreases 3 kts for every 20,000 drop in weight, so we can take that 118 down to 115. I forget whether Vref is 1.2 or 1.3 times stall. Let's use 1.2, which would put the stall at 96. I would imagine a -400 is comparable insofar as these speeds are concerned, but I don't know.
How about one-time-use arresting gear of some sort on the last 400 meters of runway?
You could drop some more weight by taking out one engine. 747s regularly do 3-engine ferries. It's no big deal. However, I'm not sure if the weight loss would be worth losing the reverse thrust of the engine being taken out. There is a lateral imbalance consideration there, but 747s used to carry a spare engine in a pylon under the wing, so if you removed an inboard engine, I'm guessing you could live with the imbalance.
Speaking of reverse thrust, it used to be for the 747-200 that the published figures for minimum landing distance were brakes only, no use of reverse thrust. If that's the case for the chart shown in the previous answer, the figures there can be reduced, and you would want to use FULL reverse immediately. Don't worry about compressor stalls, after all, I'm guessing you're not going to use the engines again.
Also, I'm sure there are performance figures for the effect of runway slope and headwind.
It would be a challenging situation, one of those things some crazy Aussie might try!  lol

This post is a great example how experience beats theory. I didn't know that the landing distance in manuals is brakes-only, and that changes the picture. However, in a strong headwind I would be careful to approach with only $1.2 \cdot v_{min}$. Think of the wind gradient close to the ground! And leave all engines in - the reverse thrust is worth it.

In addition to arresting equipment near the end of the runway, you might be able to add parachutes to the rear of the craft that could deploy just prior to landing.  Also, since you're modifying the craft anyway, you could add additional landing gear, which would increase braking power.  It's a lot of extra cost and modification, but you're buying a 747 and trying to put it in a difficult location - it might still be cheaper than disassembling it and shipping it from the nearest airport or water port that can deal with it.

Does reverse thrust really significantly reduce landing distance?  My impression, from various sources, is that it does not, and is used mainly to reduce wear on the brakes.

@NateEldredge The only way it could do that is if you either ease up on the brakes or spend less time on them (stop faster), right?

@NateEldredge reverse thrust is only effective at high speeds. Let's say it's a full load touchdown at 170kts, wet runway - reverse would help. In this case however, assuming a touchdown at 112kts, max braking, by the time the engines spool up the plane is already around 60~80kts, the speed which reverse is typically disengaged (they're not very useful at those speeds).

Would this be legal? There's so much regulation around flying, I would have assumed that landing on an airfield that clearly wasn't big enough would not be okay?

@raptortech97 One would probably want to include in the estimated cost of the effort whatever fines were to be expected. It might also be best to use a pilot who was not concerned with loss of license, maybe a retired guy who would do it primarily for the challenge, or bring in a foreign pilot who would conveniently disappear afterwards.

@raptortech97 I believe that with special permissions, for one-offs, you can make all sorts of flights that wouldn't normally be allowed. For example the three-engine ferries mentioned above.

"...maybe a retired guy who would do it primarily for the challenge" -- Terry, are you volunteering?  8vD

@FredLarson You know, if it was a -200 instead of a -400, and I had recently retired and thus still had real currency in the airplane, I would seriously consider it Unfortunately, though, I've never flown a -400 or a glass cockpit. I did consider getting a -400 type rating right after I retired just for the hell of it, but I couldn't justify the $20,000 price tag at the time.

@raptortech97 Generally I think that's true, though my impression of the US FAA is that they have tended to be increasingly reluctant to do so. Also, as a matter of information, at least back before I retired, 3-engine 747 ferries did not require special permission. They were in our op specs, and we did one every 6 months in the sim. There may have been a requirement that we notify the FAA after the fact that we had done one, just as after the fact we had to notify the FAA that we had done an in-flight engine shutdown.

@Terry I think the real question is how much he has to pay you.

Cant you just declare emergency and land at the field?

@vasin1987 If you declare an emergency, you can be fairly sure that the FAA (and I would guess the Australian CAA) would interview you. If in their opinion you had done so without real cause, they'd pursue enforcement action. Thus it would come down to whether the penalty in $ and/or license suspension/revocation was worth it.

No, it can't be done.
There has been a similar situation in the Netherlands. KLM donated an old B747-200SUD to the Aviodrome Aviation Themepark at Lelystad airport. Lelystad airport is a general aviation field located about 60 kilometers from Amsterdam airport and has a 4100 feet runway.
Even a stripped down B 747 would require more runway. In addition, the weight would damage the runway and taxiways at the destination since these are designed for a lighter category of aircraft.
They ended up taking the plane apart and shipping it over the canals and a lake to its final home.

Does this convert the barge to an aircraft carrier?

The charts say no, and I agree. 3000 feet is standard at a small GA airport and that's tight even for a Gulfstream. If your runway is that short have you considered the width? A 747 has 11 meters between the tires - although you might stop a lot faster with the outboard wheels in the grass it will be really difficult to move it after it stops. Only one wheel in the grass could be quite exciting.
Without running the numbers ('cause your case is well off the charts) in self-contradiction I will say that it's conceivable that if you land with NO fuel remaining, full flaps, set the mains down right on the beginning of the pavement, apply full reverse and full braking, AND do this on a day with a cooking headwind you might pull it off. Heavy rain will actually help here as a few inches of standing water on the runway will slow you down pretty fast. Of course, you have no option for a go-around. Such a landing would be illegal in almost any developed country.
Who's going to fly it? 747 drivers are used to things like 12,000 foot paved surfaces and ILS, not bush-grade airstrips in the outback. Bush pilots who think 1500 feet of pavement is a luxury typically don't know how to fly a 747. Just in case you don't know, large aircraft licenses are NOT interchangeable. You need a commercial license, ATP and a type rating. For an older 747 it's a fairly small club.
If you do go ahead with the project, call the Discovery Channel, producers of Dangerous Flights. they'll probably be interested.
Oh, and forget the parachute. I'm a master parachute rigger - anything capable of slowing a 747 will take 1500 feet just to deploy (you have to stage it). And the plane is not equipped with the necessary attachments.
Maybe a dozen JATO bottles hooked up backwards?

Re: your last point: https://www.youtube.com/watch?v=WKCl3lfAx1Q (idea scrapped because it's so dangerous)

Also, I don't think standing waste will slow you down faster...you will end up hydroplaning. In the military, we use standing waste as 'icy' when running TOLD charts, which significantly decreases braking effectiveness

You can find detailed technical specifications  for the 747-400 in this document. On page 97, a landing chart appears:

The operating empty weight (OEW) of a 747-400 (from the same document) is 394,088 lbs (178,756 kg).
Though the chart does not go all the way down to 394,088 pounds, towards the lower end of the chart, the change is almost linear, so we can get a rough estimate of the landing runway length requirement at OEW. With Flaps 30, at Sea Level, on a Dry Runway, you're looking at about a 1,390 meter requirement (about 4,560 feet).
The approximate slope of the graph is for every 100,000 pounds lost, landing distance decreases by 300 meters (~984 feet). Obviously this is not completely accurate, but for this purpose, it'll do. To land on a 2300-foot runway, you would need to lose another 230,000 pounds or so, putting the weight around 165,000 pounds. I'm fairly sure that stripping all nonessential equipment would not be enough here, and this ballpark estimate would require you to touch down brick one, with no gas, and no extra runway. Even if you could fly a 165,000 747, I wouldn't try to land it on that short of a runway.
So in answer to your question: No, I'm certain this cannot be done

For a truly one-shot deal, you don't even need "enough" runway, as long as you put enough EMAS at the end to handle the size, weight, and speed you expect to be dealing with. Sure, the EMAS itself gets destroyed in the process, but even an old 747 is probably a lot more expensive, and it is pretty well done flying at the end of this adventure, right?

5000 feet would be the minimum runway size under normal conditions and even this would be dangerous.
To land on a 2500 is possible but would require arresting equipment and a pilot with balls of steel.
If it were me, I would flood the runway with some kind of heavy mud, like drilling fluid or a non-flammable oil. That would probably do it. I would obviously do some physical calculations to make sure it would work before trying it.

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text:
What's the advantage of using short wings rather than long wings?
To clarify the question, I mean the type of wing used on a Concorde or a fighter jet, vs a glider's long and thin ones. What is the aerodynamic reason for using a short wing when the plane is faster?

Another reason to have shorter wings on high-speed or maneuverable aircraft deals with the aircraft's aspect ratio, which is the ratio between its length to is breadth/chord. Longer wings (high aspect) bend more under load, and may twist, which causes structural issues. Additionally, aircraft with shorter wings (low aspect) can roll much quicker. This means that a fighter jet with short wings may roll at rates up to 720 degrees/second while a large airliner or cargo plane may roll at 15-60 degrees per second.
A third reason is parasitic drag. From the linked wikipedia article above:

While high aspect wings create less induced drag, they have greater parasitic drag, (drag due to shape, frontal area, and surface friction). This is because, for an equal wing area, the average chord (length in the direction of wind travel over the wing) is smaller. Due to the effects of Reynolds number, the value of the section drag coefficient is an inverse logarithmic function of the characteristic length of the surface, which means that, even if two wings of the same area are flying at equal speeds and equal angles of attack, the section drag coefficient is slightly higher on the wing with the smaller chord. However, this variation is very small when compared to the variation in induced drag with changing wingspan.
  For example, the section drag coefficient $c_d$; of a NACA 23012 airfoil (at typical lift coefficients) is inversely proportional to chord length to the power 0.129:
   $$ c_d \varpropto \frac{1}{(\text{chord})^{0.129}}.$$

Since parasite drag increases with airspeed, and high aspect wings have higher parasite drag, it makes sense for high-speed aircraft to have the wing that creates less drag at high speeds, and the slower aircraft to have the wing that creates less induced drag. You can see this in a simple graphic of the drag curves:

(Since the induced drag is lower at high speeds anyway, there is little point in minimizing that, rather minimize the type of drag that is a much larger factor at high speeds)

At low airspeed, the aerodynamics of long thin wings are great. The longer and thinner, the lower the induced drag (the drag inherent in creating lift, very dominant at low speeds). However, aero requirements always seem to be contrary to structures requirements. Savings in aerodynamics are often offset by increased weight of structures, and a balance needs to be struck for the best fuel economy.

The wing shape is very dependent on the maximum design speed of the craft, roughly as follows:

Subsonic < Mach 0.6: long, thin and straight please. Induced drag is the dominant design factor.
High subsonic < M0.85: friction drag becomes more dominant, induced drag is less due to higher speed, and compressibility effects start introducing quite a bit of extra drag. Wing sweep is introduced. A long, thin, swept wing creates a high amount of torsion, heavier structure etc, so unfortunately we need to keep the wings a bit shorter and stubbier. New materials and wing profiles enable longer and thinner wings again with less of a weight penalty.
Transsonic between M 0.85 and M1.2: Compressibility is such a dominant factor that the area rule is much more important in reducing drag than the wing shape. Whichever wing shape fits the area rule is best. But fuel economy in this speed region is always questionable, either slow down like all pax planes or speed up like Concorde.
Supersonic > M 1.2. Compressibility drag is all dominant, and now we want to mainly limit this form of drag. Induced drag is of no concern anymore. A very good way of limiting shock wave drag is to make sure that all of the wing stays within the shock cone streaming from the nose tip: within this cone, airspeed is lower than outside the cone. Even for military planes where fuel economy is not the dominant design factor, the performance penalty of having the wing stick out of the shock cone is considerable.

Source

You may want to take a look at this and this but generally it has to do with the fact that many things change at super sonic speeds mainly

The primary advantage of the delta wing is that, with a large enough
  angle of rearward sweep, the wing’s leading edge will not contact the
  shock wave boundary formed at the nose of the fuselage as the speed of
  the aircraft approaches and exceeds transonic to supersonic speed.

Thanks! Though I'm not so sure what a "rearward sweep" refers to.

@EwenW. - simply, where the wings sweep to the rear (the wingtips are aft of the wing root)

The opposite of http://en.wikipedia.org/wiki/Forward-swept_wing

Short wing means less structural weight. But an airplane needs an optimum wing surface area (optimum for its weight, in other words the wing it needs to generate enough lift for the size of the airplane). So for the same lift, a shorter wing would be lighter, but study have shown that lift is not generated on the full span of the wing, so a short wing would not be efficient. A longer wing is much more efficient (generate more lift for its surface) but at the expense of weight (you need a beefier structure to maintain the integrity of the wing, so there is a sweet spot in between)

A high-aspect ratio wing is not only for slow flight.  lt work fine at high airspeeds too (so long as we are still well below the transonic range), as long as the wing is kept small enough to keep the wing loading appropriately high.  However, such a wing would already be flying at a rather high angle-of-attack even in wings-level flight at cruise speed, so there would be little room for pulling "extra" G's for radical maneuvering, without stalling the wing.
In the below-transonic speed range, high-aspect ratio wing are the most efficient wings possible at their optimum angle-of-attack, but they lose efficiency rapidly as the angle-of-attack is decreased below that optimum angle, compared to wings with lower aspect ratio.
A "Reno racer" with wings shaped like a sailplane's wings would either
A) stall (or at least enter the high-drag "mush" zone near the stall) while trying to "pull G's" during the turns (if the wings were small enough to be optimized for the straight portions of the race), or
B) suffer from much more parasite drag and therefore much more total drag than a lower aspect ratio wing on the straight portions of the race (if the wing were large enough to be optimized for "pulling G's" during the turns.)


text:
Why use plywood to hold the bearings for the airbrakes on a fibreglass glider?
The ASK-21 is mainly a fibreglass construction.
However, the bearings for the airbrakes and their control rods are fitted into small pieces (some 10 cm wide) of what seems to be plywood molded into the fibreglass.
The following picture shows the plate holding the bearing for the airbrake, seen from the rear side in the space in the fuselage where the wing spars are joined. The bolt that sticks out holds the bearing of the linkage that transfers the brake movement to the rods in the wing.

The last picture shows the bearings in the wing where the rod to lift the actual air brake is fastened.

What is the reason for this choice of material - could the bearings not be fitted into the fibreglass structure without extra pieces of plywood?

An image of the bearing would help illustrating this question no end.

In the ASK-21s I know the steel tubing is only used to integrate the landing gear. The wing box is all glass fiber epoxy.

@yankeekilo Point taken - if I can get one I'll post it.

@PeterKämpf interesting. I'll look at it in more detail when I get a chance.

Whoa - bad corrosion on the brass bushings for the speed brake. It seems you didn't dry them soon after getting soaked in rain.

This use of plywood is not ideal, but it works. The wood soaks up the epoxy and becomes an integral part of the fiberglass construction, and is easy to mold, so laying up the same geometry from glass fibers alone would be much more laborious.
Also, plywood is reasonably isotropic, at least in the two directions of the plywood layers. If you want to achieve similar isotropy with glass fibers, you need to interweave them - just wrapping one roving around the bearing will not do.
You could use other materials - aluminum would do, but doesn't bond as well to the epoxy resin. That Schleicher uses plywood has historic reasons. They used to build gliders with wood, some had steel tube fuselages, but wood was their primary construction material. When they started to build glass fiber gliders (the first was the ASW-12, which was a commercial version of the D-36, on which Gerhard Waibel cut his teeth as a glider designer and won the German gliding championship in 1964) they used what they knew best. And it worked.

I would not globally agree with "not ideal". It is a proven, robust and economic solution.

@yankeekilo; You're right, but it has lower compression strength than tensile strength. This shifts the failure point lower than ideally possible. I would prefer a metal structure welded to a large, perforated base plate which then is laminated between the layers of the glass fiber structure. In case of carbon epoxy, this metal is ideally titanium.

For some bearings, you need a sufficent thickness of the socket and supporting structure to deal with bending moments on the rods/bolts, plus you need to transfer the point loads into the wing structure.
Plywood is well suited for this task, while being lighter, cheaper and easier to build and machine than aluminum or fibre-reinforced plastics. Together with the top glass laminate you get a lightweight, yet sturdy structure (essentially a sandwich). As already stated, (ply-)wood is a surprisingly fabulous material.

Making a thick spot in fibreglass (to support a point load) is actually a little tricky.
The resin produces heat as it cures, so if you have too much in one spot it can get so hot that it produces smoke. Instead you need to build it up in layers, with a wait of a few hours between each set of layers. Too fast and it overheats, but you also can't leave it too long or it won't bond well to the cured resin. If you don't plan well, you end up working through the night.
It's much faster and easier to slap in a block of wood, and do the whole job in one go.


text:
What is the difference between stopbars and Intermediate Holding Position Lights?

I know that stop bars continuously light red and stand at before taxi route joint, holding points, or at the runway entrance, but what about the Intermediate Holding Position Lights? How can we differentiate between the  stop bar and Intermediate Holding Position Lights with regard to function and location or color? I added pictures below; I am sure of the stop bar, but am I correct about the Intermediate Holding Position Lights? Btw; there is a definition for Intermediate Holding Position Lights: A set of three amber lights or full red stop bar are provided at intermediate taxiway holding positions.

Intermediate position holding lights may be used at larger airports as an additional means of controlling traffic while moving on taxiways to give way for other surface traffic an a taxiway intersection.  Stop bars are used to provide additional identification of the boundaries of runway safety areas and ILS critical areas to prevent runway incursions.

Okay and what about the picture? Do you agree with the marking of holding light is an intermediate position holding light? Because it suits the definition above: 3 amber light.

The main difference is that stop bars are used for stopping traffic from blocking ILS signals for traffic inbound on near runways, and intermediate position holding lights are used for holding short for taxiways.
Pretty sure your image has that explained already.

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text:
Is there any current knowledge of a 747 being used as a drone for military applications?
ex. direct action, reconnaissance
Current military drones usually carry 4 hellfire missiles. If the military used a 747 drone the payload capacity could increase by a factor of 10.

Only a factor of 10?

Probably all it could be good for, B-52 can also do.

There are no known 747s being used as drones, nor is there any public program to do so. Sure a weaponized 747 could carry a lot of missiles. Actually, there was a proposal to convert 747 into a missile carrier, called the Cruise Missile Carrier Aircraft or CMCA (it was manned though). And the factor of 10 is pretty conservative.
The CMCA was expected to carry more than 70 Air launched cruise missiles, specifically the AGM-86 ALCM.

Image from foxtrotalpha.jalopnik.com
The idea was to modify the nose loading 747-200C, with nine rotary launchers mounted on tracks inside of the stripped-out cabin. Each rotary launcher would hold eight missiles, and they could be slid back into a launching position at the rear right side of the aircraft through an overhead handling system.
A bay door on the right side of the 747's tail cone would open and an ejector system would launch the missiles either singly or in a salvo.
The idea was proposed when the B-1 was canceled and died when it was revived.


text:
What is the process to remove frost off an airliner?
My aunt recently was going on a flight home and she boarded the flight, but her flight was delayed due to frost on the aircraft. She noticed this crane like device above the aircraft wing during the removal process. How do they remove frost off an airliner?

I couldn't find any good tags for this question. If you guys find any tags that would fit with this question then go ahead and add it in, and you probably want to delete my frost removal tag.

On Youtube: Aircraft Deicing Philadelphia International Airport (and many more linked).

@Simon Sort of...  Frost can form even on very hot days (due to cold fuel in the wings).  While the answers apply, the linked question isn't quite a duplicate, especially since it isn't even always required to remove frost in the first place.

Frost is removed through the application of (typically) Type I de-ice fluid (information about de-/anti-ice fluids). Fluid application is generally from a truck with a lift so that the operator can spray the aircraft from above. The fluid is generally hot, diluted with water and under pressure so you'll see lots of steam coming off of the fluid spray. The truck will drive around the airplane spraying the wings, tail and fuselage as necessary to completely remove snow, ice and frost.
Some airports have static mounted de-ice towers that are more like cranes and some operators have automated trucks where there is no operator in the lift and they can do the whole operation from the cab of the truck.


text:
How likely are flares to be fire hazards once touching the ground?
According to the Wikipedia page of flares, flares create intense heat.

A flare, also sometimes called a fusee, is a type of pyrotechnic that produces a brilliant light or intense heat without an explosion.

Could the flares launched by an aircraft as a defensive countermeasure against a heat-seeking missile cause a fire once they reach the ground?

Any pryotechnic released close enough to combustable materials will combust, I'm not sure what the question is? Are you asking if the flares are flame-resistant? Are you asking if they are designed to extinguish before hitting the ground? Are you asking from what altitude they can be released without touching the ground in a combusting state?

I'm wondering if the event of a fire starting on ground due to flares launched from above (Likely due to flammable terrain such as a forest) has already happened.

Not really an aviation question....

I have no idea how likely it is general, but it seems that flares are indeed sometimes blamed for causing wildfires on the ground.
In New Jersey (2007):

A massive wildfire that has already burned thousands of acres in the
  Pinelands and forced the evacuation of residents in two towns likely
  started this afternoon when an F-16 fighter jet dropped flares as part
  of a maneuver over a gunnery range, New Jersey National Guard
  officials said tonight.
[...]
"We believe it was one of our F-16s on a routine training mission that
  dropped the flare that started the fire," said Lt. Col. James Garcia,
  a spokesman for the state Department of Military and Veterans Affairs.
  "There's going to be an investigation."

In Oregon (2017):

A remnant of a military flare was found at one of the areas burned,
  triggering a call to the Air National Guard, which uses flares in
  self-defense training exercises over those same areas that burned.
  Flares are deployed in air combat to draw heat-seeking missiles away
  from their targets.
After being contacted by investigators about the fires, the Oregon
  National Guard agreed to suspend the use of flares. Agencies also
  engaged them about mitigation techniques to employ if it is determined
  that the guard was the cause.


text:
In the US, do ultralight aircraft have tail numbers?
Just wondering if ultralight aircraft in the United States have tail numbers like the larger general aviation aircraft have?

Drones have them too.

@RonBeyer Drones don’t have tail numbers like larger GA aircraft, but if they are flown under the Small UAS Rule (Part 107) they are required to have their FAA registration number marked on them. https://www.faa.gov/uas/getting_started/registration/media/UAS_how_to_label_Infographic.pdf

Assuming that you mean an ultralight as defined in part 103, there is no requirement to be registered or have a tail number. 14 CFR 103.7(c) says:

Notwithstanding any other section pertaining to registration and marking of aircraft, ultralight vehicles are not required to be registered or to bear markings of any type

In the USA: "ultralight aircraft" as in having an engine or two? Yes they do.  Pretty sure anything larger than an 8 oz drone needs to be registered to fly in the US airspace. Hang gliders and parachutes are about the only thing not needing a tail number.  I'm sure someone here can find the appropriate FAR paragraphs with the details from www.faa.gov  My internet is awfully slow today.
I may have overstated things above. Found this article at the United States Hang Gliding and Paragliding Association website, which seems to state that "true ultralights" may not need to be registered, and has quite a few reference links at the bottom:

January 31, 2008 is the deadline for converting overweight or two-place ultralights used in our current fleet of tugs to FAA-registered E-LSAs. After that date, it will not be possible to convert an existing unregistered tug to an E-LSA. An overweight or two-place ultralight tug that is not converted to an E-LSA by January 31, 2008 can continue to be flown until January 31, 2010, but after that date that it cannot be flown at all, as the FAA will consider it to be an unregistered aircraft without an airworthiness certificate. Very light tugs that actually meet the definition of a true ultralight may continue to tow hang gliders under Part 103 rules, without being N-numbered, as long as USHPA's aerotowing exemption #4144 remains in effect.


text:
What is a "flare-out" and why does auto-thrust reduce thrust during flare-out?
The functions of auto-thrust include thrust reduction during a flare-out. What is flare out and why during flare out will the auto-thrust reduce thrust?

The proper term is "flare" not "flare-out".
"Flare" is a term used to describe the act of raising the nose of an aircraft in order to increase lift and stop descending in order to land on a runway smoothly.
Whether the pilot, or Auto Thrust does it, a reduction of power to idle is needed in order to bleed off the excess speed that is used during the approach phase.  If the thrust is not reduced to idle, the aircraft will take longer to land, and use up more runway.
If you don't flare enough, the rate of descent will be too high and the aircraft will land hard.
Too much flare will make the aircraft climb back up.

The objective is to land smoothly, that is reducing the rate of descent which is still about 700 ft/min, 400 to 500 ft above ground. Landing with this rate is quite hard, so we need to reduce this rate of descent before touch down.
The usual way is to lift the nose, thus increasing the AOA, therefore increasing the lift but not to a point of climbing, so a speed reduction would be simultaneously required. Thus reducing the thrust is needed. Happily this is very helpful if thrust reversers are used once on the runway, since reversing requires the transition through idle.

Are you talking about a "flare"? Or a "flame-out"?
A flare is part of the landing sequence. You raise the nose of the airplane so that you touch down gently on the main gear. The engines need to be at idle (or at least, low thrust) at or before that point because the whole point of landing is to come to a stop.
A flame-out is what happens to a turbine (jet) engine when it doesn't get enough fuel to sustain combustion. In this case, the thrust is lost because the engine is no longer running, not because of anything the autothrottle did.


text:
Am I allowed to replace my own Model A-30 Altitude Digitizer?
My Transponder Mode C (Altitude Reporting) function quit working.  The position reporting function is working fine.  I believe the failed component is the self contained Model A-30 Altitude Digitizer "box" that is bolted to the interior of the fire wall.  It has a connector cable to the transponder and a rubber pitot tube connection.  I am an Aerospace engineer with 32 years experience designing and testing Space Shuttle Main Engines and components.  I have done my own annuals and had my local FBO mechanic inspect the work and sign it off.  The replacement of the Altitude Digitizer box does not require the removal of the transponder - just bolt on the new box and re-connect the air tube and plug in the "D" connector to the transponder.
As the aircraft owner would that be approved for me to do as a non-complex assembly/maintenance?  I know the calibration would have to be done by my certified avionics shop personnel, but can I do the R & R of the box?  Having my avionics shop do it adds another \$200.00 to the calibration cost of $175.

Before replaying the box, verify that the cable to the transponder is in good condition. The Mode C code is a Gray code that is transmitted over a parallel cable in some older model encoders / transponders. If the cable is not connected properly in the socket or has damaged internal wires you will get some wrong altitudes and big jumps in altitude reporting.

Per 14 CFR 43.3(d):

A person working under the supervision of a holder of a mechanic
  or repairman certificate may perform the maintenance, preventive
  maintenance, and alterations that his supervisor is authorized to
  perform, if the supervisor personally observes the work being done to
  the extent necessary to ensure that it is being done properly and if
  the supervisor is readily available, in person, for consultation.
  However, this paragraph does not authorize the performance of any
  inspection required by Part 91 or Part 125 of this chapter or any
  inspection performed after a major repair or alteration.

This means if you are not a mechanic yourself, you can still perform this work as long as it is supervised by someone who is authorized to perform the work. Based on your question, I assume that you actually want to perform this work yourself.  Further down in 14 CFR 43.3(g), the FARs state the type of work you can perform without supervision:

Except for holders of a sport pilot certificate, the holder of a pilot
  certificate issued under part 61 may perform preventive maintenance on
  any aircraft owned or operated by that pilot which is not used under
  part 121, 129, or 135 of this chapter. The holder of a sport pilot
  certificate may perform preventive maintenance on an aircraft owned or
  operated by that pilot and issued a special airworthiness certificate
  in the light-sport category.

Preventive maintenance is defined in  Appendix A to 14 CFR 43, paragraph C. If a function does not appear in this list, it is not preventive maintenance, and as such must be performed by personnel authorized to perform repair work. The only item in this list that is even remotely relevant to your situation is item 31:

Removing and replacing self-contained, front instrument panel-mounted
  navigation and communication devices that employ tray-mounted
  connectors that connect the unit when the unit is installed into the
  instrument panel, (excluding automatic flight control systems,
  transponders, and microwave frequency distance measuring equipment
  (DME)). The approved unit must be designed to be readily and
  repeatedly removed and replaced, and pertinent instructions must be
  provided. Prior to the unit's intended use, and operational check must
  be performed in accordance with the applicable sections of part 91 of
  this chapter.

Note that your situation does not appear to qualify, because the item you are replacing is not part of a self-contained, tray-mounted device.  Even if it were, you would still not be authorized to perform the work because this item specifically excludes work on transponders.
Of course, I am not an attorney nor do I perform aircraft repairs, so my interpretation is completely non-qualified. For the best answer, I would suggest contacting your local Flight Standards District Office for guidance.


text:
Laser projection on the sky
Suppose that one points a laser beam to the sky, constantly (so that an aircraft have to deal with it).
Could that beam cause any trouble to that aircraft?
Would that individual need to obtain some sort of authorization?

Yes, pointing a laser at an aircraft poses a serious risk to those on it, please don't do it. See the link in the comment above.

@ratchetfreak that question deals with "why", this one with "if". There are instances of lasers constantly shoot at the sky, and powerful ones even: http://www.eso.org/public/images/potw1425a/

and the accepted answer addresses both (only aircraft within 12k feet will be hindered by a green 5mW laser)


text:
How is the lighting panel of an Airbus A340 designed and how does it work?
I'm trying to simulate the light switch panel of an Airbus A340 with real electronics components for a model in scale (I'm doing the electronics lights with leds).
Taking a look at this PDF (page 129), I would imagine that there are several switches for these lights. But when I searched on Google Images, I couldn't find a photo of this panel, only some diagrams of A320. I never saw one that I could identify.
Question:
How is the light switch panel and/or where can I find a picture or diagram?
UPDATE 1:
Is it something like this?

UPDATE 2:
I'm seeing that some switches have 2 or more points? For example NAV & LOGO, what means 1 and 2? Off, NAV or both?
And what about STROBE-BEACON, what does "AUTO" mean?
By the way, I couldn't find the "CARGO" light, and I think that "DOME" are the Landing Gear Bay, but what does BRT/DIM mean?
UPDATE 3:
I was reading this:
AIRBUS A340 - Flight Deck and System Briefing for Pilots
But I couldn't find an image about the navigation panel.

I believe "dome" means cockpit ambient light; "brt" ("bright") means higher intensity and "dim" means lower intensity.

Nav and logo.
The logo light is a spotlight which illuminates the tail to show the airlines logo at night.  The Airbus A340 has two circuits for NAV/LOGO. Logo is an auto option when the landing gear is not compressed or the flaps are extended at 15º or more." in both positions, 1 and 2.
Dome is the cockpit ambient lighting.
Strobe on means the strobe is lit.  Auto means that the strobe is on when the landing gear is not compressed - i.e. it comes on just at the point of take-off and switches off on landing.  The point of having "on" as well is that some procedures require the strobe to be turned on just before entering the active runway and when leaving it.
Hope this helps.
Picture of the panel:

thanks a lot! And the distribution for airbus a340, is that? Where can I found a picture or diagram about that? thanks in advance!

@LeandroTupone Do you mean a wiring diagram?  I don't have those.

No no, like the image I post, a diagram on how there is the panel. Or a pic

Sorry for my vocabulary, I'm not an english native speaker

Actually I was reading that airbus a340 has two circuit for NAV/LOGO so that's why are 1 and 2. LOGO is an auto option "when the main gear struts are compressed or the flaps are extended at 15º or more." in both positions, 1 and 2

@LeandroTupone Please never apologise for your vocabulary.  The problem is mine to ask questions to clarify since your English is very much better than my Spanish.  It seems that I was wrong about the nav/logo and you have accurately answered your own question.

@LeandroTupone This picture is high resolution so you can zoom in and see it it really looks.  Is this what you needed?

Simon, you rocks!!!! That was I was looking for!!! THANKS A LOT

I found it, specifically for A340, page 11 of this document:
http://www.smartcockpit.com/aircraft-ressources/FCOM_A340-Lights.html

Please see the comments of the Simon answer, who post a very good photo of the panel !


text:
Is there a worldwide association for stunt/trick/tournament hang-gliding?
I'm wondering if there is any prevailing organized body of sports-people in hang-gliders, other gliders, and/or personal non-powered glide craft in general?
I'm particularly interested in stunts related to gliding, competitions, and how to find people in each locale (presumably) thorough an 'organized' body of sports-people.

FAI's aerobatics committee might be a place to start. In general, FAI takes care of worldwide airsports matters.

FAI (Fédération Aéronautique Internationale)

– The World Air Sports Federation, is the world governing body for air
  sports, aeronautics and astronautics world records. Its head office is
  in Lausanne, Switzerland.[3] This includes man-carrying aerospace
  vehicles from balloons to spacecraft, and unmanned aerial vehicles
  (such as model aircraft and UAVs). It was founded on 14 October 1905.

FAI is the international governing body for Acrobatics through its FAI Aerobatics Commission("Commission Internationale de Voltige Aerienne" – CIVA).
For Gliding through FAI Gliding Commission("International Gliding Commission – IGC").
For Hang Gliding and Paragliding through FAI Hang Gliding & Paragliding Commission ("Commission Internationale de Vol Libre – CIVL)

I have learned of an organization that calls itself the International Aerobatics Club.  It seems to be a US-based competition group, which prepares teams for international competitions.


text:
Why do airliners have to file delays through their handlers?
Often when listening to ATC (commonly Dublin), when an ATP requests push and start, the controller will reply, "You have missed your pushback window", and/or ask the pilot to call their company or handler to "file a delay" or "update your flight plan with your off-blocks time".
I have two questions about this but I expect the same answer answers both.

Why is it necessary to re-file the plan, rather than simply activating the flight plan with the actual departure time?
Why is it necessary for the pilot to change to the airline's frequency, chat them up, change back, and then wait for the electronic flight plan to be updated, rather than talking to the controller directly?

Since you mention Dublin, I am going to give an answer that describes the situation in Europe. Other parts of the world may have different procedures, although I believe they will be similar.
Usually a flight plan must be activated within a given time window to ensure that there is enough capacity (airspace, ATC staffing, departure & arrival airport constraints) along the route to handle the flight. If the flight is not departing with this 'slot' a new flight plan needs to be requested and approved by the Network Manager Operations Centre (NMOC) (Previously called Central Flow Management Unit (CFMU)).
The controller is not responsible for filing flight plans and cannot be tasked with doing the paperwork for the crew. The crew therefore needs to contact their handler or flight operation centre to refile a flight plan.
The NMOC will reassess the flight plan and verify that there is capacity along the planned route to handle the flight. If there isn't, the flight may need to be planned along another route or an additional slot delay will be given.

I believe the NMOC/CFMU is unique to Europe. Western Europe is one of the busiest airspaces, so the rules need to be stricter than in other parts of the world.

wrt paragraph 3, ATC often can technically send a delay message from their system quite easily, but often don't want to do so. Some airlines and/or airports prefer to do it themselves to keep track of changes. Or the controller might simply just be too busy. The rule book says ATC is responsible for sending delay messages when the aircraft has started taxiing - before that, technically not ATC's problem


text:
Do military pilots have a phrase like "aviate, navigate, communicate"?
The phrase "aviate, navigate, communicate" is commonplace among pilots, as a reminder to concentrate on flying the aircraft first, with navigation a secondary focus, and fitting in communication when it won't interfere with those other things.
Military pilots have other things to distract them from the primary focus on flying: tracking the target they want, keeping an eye out for other threats (not just collision threats), managing EM emitters or countermeasures, &c. Flying into a bad situation due to "target fixation" is not uncommon.
Do military pilots have any kind of drill, phrase, mnemonic, or teaching aid to set priorities for their flying, like "aviate, navigate, communicate"? To be clear, I expect they use that phrase for 'normal' flying, and I'm curious to know if there's an extra mnemonic about their combat-specific priorities; maybe something like "wingman, threats, targets".

"aviate, navigate, communicate" is applicable to 99.99% of military flying, but that 0.01% is where it gets interesting.

I don't know if the military does this, but when I flew GA aircraft my instructors always told me "fly the airplane" first, no matter what. The only exception was a fire - then priority became put the fire out, then fly the airplane.

In the UK, initial military flight training is in fact contracted out to non-military training organizations, so it would be rather surprising if the initial training methods and objectives were significantly different for military and non-military students - especially since one of the justifications for the subcontracting was that they were not different.

The military and civilian community overlap significantly. They largely use the same curriculum for basic flight skills.

I imagine this is one of the phrases that came to civilian flight training by way of military folks moving in to the civilian realm as instructors. Even in the context of "Wingmen, Threats, Targets" you're still operating under the overarching theme of Aviate (Wingmen - remain in formation, don't hit each other ; Threats & (air) Targets - evade or engage, again without hitting each other), Navigate ((ground) Targets - finding your way to them ), Communicate (Wingmen - Issuing/acknowledging orders ; Communicating with C&C/ATC, etc.)

Military pilots have other things to distract them from the primary focus on flying - civilian pilots also have a high number of external stresses and distractions.  Many will have more distractions from the primary task than some military aviators (remember, most military pilots are not fighter pilots). Aviate navigate communicate is in the heart of every aviator.

@GdD That 0.01% is covered by another one of my favorite sayings I believed coined by Harry Copland, "There are old pilots and there are bold pilots, but there are no old, bold pilots" It wasn't the young aviator new to the ship, or the old hand that the CAG worried about, but the intermediate pilots, maybe on there second cruise, who believed they had seen it all.

I am a Naval Aviator and have commanded a flight training squadron.  We actually teach that very phrase.  Aviate, navigate, communicate was one of the first things I learned, and it has served me well over the years.
It applies no matter the situation.  The target fixation example you gave is a good one.  Getting an aircraft where it needs to be to put a bomb on target is clearly in the navigate realm.  It is superseded by not flying into the ground...which is in the aviate realm.

In a combat situation, the "aviate" is a bit more complex than normal flying because energy management is part of aviate (in a sense, it's similar to the mindset of glider pilots)

And flying into the ground is precisely what the adversary will try to make you do. Somewhat famously an EF-111 (unarmed) scored a victory that way in Iraq (in the first war)—they got under attack, evaded down and the Iraqi was too fixed on getting a lock and failed to pull out behind them.

I am a former USMC helicopter pilot and after 20 years I still remember that very phrase - and used it to teach my kids to drive. Yes, it is a phrase used by military pilots and, given its value, I am sure it is used by pilots in general. The general concept is "don't fly into something or fly into a situation where your wings/rotors get ripped off because you were trying to talk to someone or figure out where you are as opposed to where you are supposed to be." If you aren't flying the bird, nothing else matters. If you are flying the bird but don't know where you are/are going, then nothing you can tell others matters.

Is it really a good guide for driving a car? Does continuing to drive the car really take priority over lookout?  Just wondering what the relative priorities should be :)

@Andy - I always tell my kids, there is more than one way to get anywhere. If you miss your exit, don't come to a screeching halt in the middle of the interstate (as I have actually witnessed someone do) just to get over to the exit lane, or otherwise freak out. Drive safely to the next exit and turn around, or come up with an alternate route. This falls squarely into the same advice - operate the vehicle safely first, then worry about the route. Clearly, this also means you should be planning ahead so you know where the exit is, but there can be many reasons you don't actually exit there.

Thanks that makes sense. (i.e. The first word covers all aspects of safe & sensible operation, not just driving!)

In the car realm, "aviate" means driving the car safely - including keeping a safe lookout to make sure you don't run into anything, navigate means just that - navigation - if you miss your exit, don't panic and start looking at the back window at where you wanted to be, just drive the car and when convenient figure out how to get back to where you need to be. Communicate.... tell other drivers what you're doing through turn signals or tapping the brakes when you see a slowdown ahead.

@Johnny Great point. I didn't really address Communicate, but many accidents and other problems occur when you do something unexpected.

@GalacticCowboy relevant (Louis CK): https://www.youtube.com/watch?v=CQSRPMFDTSs

@Johnny: While I agree with both you and Taylor's answer, and while this isn't about street safety in the first place, let me suggest to put the operation of turn signals into the "aviate" / "driving safely" section, as "non-optional communication". Not communicating in an airplane for a minute or two is not that much of an issue. On the street, you don't have that much separation to work with, so flash those lights, early and always! "Communicate" is about telling your passengers what you're doing, or talking to them, full stop. It's somewhat hard to drive safely without turning lights.

I went through US Navy aviation training and never heard the phrase. Spent many years in the fleet and never came across it either. It was just the pilots I met on the way through, and the conversations we had, just never came up. It still surprises me to this day. It is possible I missed it in some training manual too. But it is the kinda phrase that you hear, and without any experience, understand implicitly the wisdom behind it. In my opinion, St Exupery's Wind, Sand, and Stars is the heart and soul of this phrase. Maybe I never heard it because I had found it before I ever began to fly.
I am thankful to the pilot who shared it with me. I was a cadet at the US Merchant Marine Academy in my junior year when I sat down in the NROTC class I was required to take. I was an engineer and the class didn't have much appeal for me. But that day was different. We got to sit through a movie about carrier aviation, and I remember watching the jets landing on the ship thinking, "I am going to do that."
I went to my NROTC Department Head and told him about my decision. I remember him telling me, "You just aren't the type." To his credit, when I told him that I didn't care, he did all he could do to get me into carrier aviation.
I was working in one of the academic buildings after hours one day a year later when I started up a conversation with a man I met in the hallway. Not sure how it all took place, he wasn't an instructor there, but I do remember telling him about my plans after graduation. He mentioned that he was a production check pilot for fighter jets coming of the manufacturing line on Long Island. We talked a while, and then before he left I asked him, "If you had one piece of advice to give me before I start to fly what would that be?"
He said, "Aviate, Navigate, and Communicate!"
It was the best advice I ever got, except for "If you find your dive angle over 15 degrees in a pop-up delivery pull out immediately." It was my mantra and I am thankful that he passed it on to me.

For carrier landings the neumonic, (or mantra) to help with priority and scan was “meatball, line-up, angle of attack”.  This was taught from day one of Field Carrier Landing Practice.  LSO instructors reinforced this theme throughout training, and into the fleet.
MEATBALL:  This is in reference to the orange colored ball on the Fresnel lenses optical landing system, that displays glideslope in reference to two horizontal rows of green datum lights on either side.
LINE UP:  Self explanatory, but especially critical for larger wingspan aircraft.
ANGLE OF ATTACK. AoA indexers on the glareshield showed an amber donut when on-speed, a green chevron when slow, and a red chevron when fast.
The indexers could be noted in your peripheral vision, line up was crossed checked periodically, so most of your scan was dedicated to using throttle to hold the ball in the center.

This might be better suited as a comment.  Could you back it up with some sources and include a little more information?

@dalearn, I beefed up my answer a bit.  You might be able to find a reference in LSO NATOPS, but it is cultural, and based on personal experience.  Not something anyone can see for themselves in the AIM...

Thanks!  Looks good!

In my airforce this is also a useful technique that is thought to assist in handling emergency situations, at least initially. Often it would be followed by other models to assist in dealing with the emergency. It reminds you not to get so distracted by "handling the emergency" that you end up flying into the ground or not routing to a safe area to land or eject. Once you have control of the situation communicate your problem and intentions to ATC who can assist and/or get emergency vehicles on standby. So similar to the previous answers but with more emphasis on an emergency situation.


text:
Why did the AvroCar fail to fly above 3 feet?

I don’t quite understand why the AvroCar didn’t reach more than 3 feet? Was it a ground effect keeping it at that height and it didn’t have the capability to fly higher?

From what can be gleaned from the Net, it was instability. The Avrocar had plenty of power but was unstable. The resulting behavior made it uncontrollable when leaving ground effect. In this publication I found an illustration which tries to explain what went on:

Any asymmetry in flow would shift the center of pressure, resulting in a wobbling motion called hubcapping (because it resembled the motion of a hubcap when dropped to the ground).
From the linked document:

On September 29, the ﬁrst attempt of sustained ﬂight was made with the Avrocar pinned to the ground by cables. After that the vehicle took off, an uncontrollable oscillation occurred with each wheel alternately bouncing on the ground. […] These ﬁrst captive ﬂight[s] revealed then a new problem, called “hubcapping” which has never been fully resolved. The hubcapping was rapid and unpredictable swings in pitch and roll axes.

I once had a teacher who worked on the program as a technician at Avro Canada. If it was designed today with modern synthetic stability they might have something.  But even then I expect the overall efficiency would be way less than a regular helicopter from a lift perspective.  A lot of it seemed to just be that 50's infatuation with "flying saucers".

@JohnK: Conventional aerodynamics tells us that the center of pressure on a circular wing is at 24% of the mid chord. If you want to change direction without rotating the disc, half the lift must be added by vertical blowing over the rear half to balance the craft. Even with fast, digital flight controls the amount of control power needed makes a flying saucer simply not worth it.

Your point is taken but in the Avrocar's case the body was never intended to function as a circular wing, as there was no means to propel it along so that the body could operate at an angle of attack like an airfoil.  The center fan driven by the exhaust of the 3 tangential turbojets buried inside produced almost all of the lifting force, blowing straight down, and the air diverted directed out around the D shaped ring and duct was for supplemental lift and attitude control. To gain speed it had to tilt the body to tilt rigid fan's thrust vector. In effect a kind of bizzaro-world helicopter.

@JohnK: Even if it is not intended to produce aerodynamic lift, it will do so if given the angle of attack. So the slightest misalignment with the zero-lift angle will produce highly destabilising forces. What a concept!

It might have worked if they have made it completely unaerodynamic like this one, which predated any computer control system: https://www.youtube.com/watch?v=f8W2SI4c93s.

Anything produces aerodynamic lift if it's going fast enough ;)


text:
Why did the Solar Impulse flight take so long?
The Solar Impulse just made big news for flying from Japan to Hawaii on a solar-powered plane in five days.
But five days seems really long. Let's do the math on that. The distance from Japan to Hawaii is about $6,611 km$, so $6,611 km/5 days/24 hours = 55km/h$
So it was flying an average of $55km/h$? That seems too slow to maintain lift.

I added some more info.

The plane didn't fly in a straight line, due to the need to evade weather and to deal with prevailing winds. It also needed to circle a bit before landing because it arrived in very early morning when it was too dark. Actual distance covered (and average speed)  was therefore a bit higher but still under 75 km/h)

No, it could not fly much faster with the available energy.
Lift is a question of wing area and dynamic pressure. Solar Impulse 2 has 269.5 m² wing area to carry its 2.3 tons of mass. This is a wing loading of just 8.53 kg/m²; much less than even gliders have (they start at around 30 kg/m²). This allows it to fly very slowly; if we assume it flies at the lift coefficient $c_L$ for optimum range for propeller aircraft
$$c_L = \sqrt{\pi \cdot AR \cdot \epsilon \cdot c_{D0}}$$
and guess the zero-lift drag coefficient $c_{D0}$ to be 0.029 and the aspect ratio $AR$ to be 19.18, the result is 1.377. This is already close to the maximum lift coefficient, which I expect to be 1.6. Now we need the lift equation to calculate the speed which is needed to keep it flying at this lift coefficient:$$v = \sqrt{\frac{2\cdot m\cdot g}{c_L\cdot S\cdot\rho}}$$
Let's assume it flies in 9000 m altitude where air density $\rho$ is only 0.4671 kg/m³, the result is 16.13 m/s or 58 km/h. Now consider that it will fly at the beginning, late at night and at the end of the flight at lower altitudes, and may not be able to fly a straight course (maybe to fly around bad weather), and the 55 km/h look entirely plausible, if not outright speedy. At sea level, the optimum range speed is only 9.96 m/s or 35.86 km/h, just about its take-off airspeed.
Flying faster would need more energy and would not allow Solar Impulse 2 to recharge its batteries for the night hours. Solar flight must be slow to be possible at all.

From here
Solar Impulse Performance

Solar Impulse can fly at the same speed than a car, between 36 km/h
  (20 Kts) and 140 km/h (77 Kts).
At sea level: minimum speed of 45 km/h (20 Kts) and maximum speed of
  90 km/h (49 Kts). At maximum altitude: from 57 km/h (31,5 Kts) to 140
  km/h (77 Kts).

From here
Wired.Com article, interview with pilots

“You have to react quickly because if you go down 50 meters, you reach
  the maximum speed,” he says of the design limit of the airplane. “If
  you go up 50 meters you reach the stall speed.”
The calculated maximum speed is 44 knots (51 mph), but the pilots
  limit themselves to 35 knots (40 mph). The stall speed — the point at
  which the airflow separates from the wing and it no longer generates
  sufficient lift — is just 19 knots (22 mph).

Thanks. I didnt realize that an aircraft could fly at such slow speeds.

You're welcome.  It has massive wings.  The wing area is a key factor in the lift equation.

@David It turns out that all solar-powered airplanes are quite slow. I've even seen video of someone following one down a runway during its takeoff run... on a bicycle. Solar energy density is actually quite small. While peak solar power density when the sun is directly overhead and there are no clouds is about 1 kW per square meter, overall average solar power density at the latitudes where most humans live is only 100-200 W (0.1-0.2 kW) per square meter. For reference, that's almost enough to power my video card... and that's even if you have 100% efficient panels (which no one has.)

@DavidGrinberg : there are even conventional aircraft which can fly that slow, even slower. The Antonov 2, an almost 70 year old plane, for example, can fly so slowly that its manual doesn't even specify a stall speed! You can fly controllably at 40 km/h, and if you fly any slower, you'll just descend like with a parachute.


text:
What is the white pattern on trim wheel for?
On a A320, there are white patterns spread regularly on the trim wheel (highlighted on the right of the picture). First I though it was to have visual feedback about THS (trimable horizontal plane) position. But looking closely, this role seems to be played by the graduations (highlighted on the left of the picture).

(photo #0393544 from airliners.net)
Why are there those white patterns on the trim wheel? What is their role?

The White patterns on the A320 family Pedestal are provided to give the pilot an indication that the Wheel is moving, especially during a flight where your CG (center of gravity) is constantly moving.
secondly, as part of ROT (rule of thumb), each white pattern corresponds to a change of 0.2 degrees on the THS. there will always be 5 white patterns visible to pilots to give a change of 1.0 degrees on the THS (trimmable horizontal stabilizer)
if it was moved by one complete cycle

Picture ref:https://www.airliners.net/photo/BMI-British-Midland/Airbus-A321-231/727825/L

The white marks make it easy to see if the trim wheel is moving, which would be tricky if it was entirely black.
But wouldn't the pilot always know if they was spinning the trim wheel? Remember that the autopilot can also adjust the trim, which might not be obvious to the pilot. The visual marks make it easy for the pilots to see what the autopilot is doing.
Example video (not an Airbus, but very similar):

Not just the autopilot, but the electric trim on the yoke. The pilot can verify the trim is moving when the button is pushed.

Could this not be seen thanks to the graduations?

@ManuH It is a different scale. The actual trim wheel will spin many times to go from one end of the scale to the other. So smaller changes would not be obvious just by looking at the scale.

@ManuH: As you said, “ looking closely”, but the pilot can't always look closely at that specific graduation.

GIFs: https://i.sstatic.net/jQjVP.gif from here and https://i.sstatic.net/nqTgg.gif from here

Wait a minute? The A320 trim wheel automatically moves through autopilot control? I always thought they were simply a manual trimming device, basically for takeoff trim and degraded systems situations. Can someone confirm that the A320 trim wheel moves due to autopilot commands?

If I understand correctly, I think you may add a little sentence about highly contrasted objects moving in peripheral vision.

@DaG disclaimer: I'm not an airline pilot, thus I can't imagine how it looks like when riding such plane for real (but if I would like to)